The present invention relates to components of catalysts for the polymerization of olefins CH2xe2x95x90CHR, wherein R is hydrogen or a hydrocarbon radical having 1-12 carbon atoms. the catalysts obtained therefrom and their use in the polymerization of said olefins.
In particular, the catalyst components of the present invention are very suitable for the preparation of crystalline propylene (co)polymers by using gas-phase, slurry or bulk (co)polymerization processes.
Components of high-yield catalysts for the polymerization of olefins, and in particular for propylene, are known in the art. They are generally obtained by supporting, on a magnesium dihalide, a titanium compound and an electron donor compound as a selectivity control agent. Said catalyst components are then used together with an aluminum alkyl and, optionally, another electron donor (external) compound in the stereospecific polymerization of propylene. Depending on the type of electron donor used the stereoregularity of the polymer can vary. However, the stereospecific catalysts of interest should be able to give polypropylene (co)polymers having isotactic index, expressed in terms of xylene insolubility, of higher than 90%.
Said catalyst components, and the catalysts obtained therefrom, are largely used in the plants for the (co)polymerization of propylene both operating in liquid phase (slurry or bulk) and in gas-phase. However. the use of the catalyst components as such is not completely satisfactory. Indeed, problems such as formation of polymers with irregular morphology and in particular of fines and low bulk density are experienced when plants operate with catalyst components as such.
In order to solve these problems, the catalyst components are often pre-polymerized under controlled conditions, so as to obtain pre-polymerized catalysts having good morphology. After pre-polymerization, the catalysts also increase their resistance in such a way that the tendency to break under polymerization conditions is decreased. As a consequence, the formation of fines is reduced and the main polymerization process, either in slurry or gas-phase, can be carried out smoothly and with the production of final polymers having high bulk density.
However, one of the possible drawbacks associated with this method is the lowering of the activity expressed as amount of polymer obtained per g of catalyst fed. In other words. even if the activity of the catalyst in itself (expressed in respect of the magnesium chloride contained in the catalyst) could remain at the same level, the activity in respect of the pre-polymer/catalyst system, is lower due to the effect of the dilution of the catalyst within the pre-polymer. Depending on the degree of pre-polymerization, the loss in activity can also be substantial. This means that a large amount of pre-polymer/catalyst system must be fed to the reactor in order to obtain acceptable yields. It would be therefore important to have a pre-polymerized catalyst component in which this drawback is absent or minimized.
In the international patent application WO95/26369 the pre-polymer obtained by pre-polymerization of a catalyst component comprising a Ti compound supported on magnesium dihalide. is contacted with a metallocene compound in particular selected from the class of zirconocenes. The resulting catalyst shows a good activity with respect to magnesium chloride therein contained but the yield is rather low if referred to the pre-polymer/catalyst system. In any case, the catalyst obtained after treatment with the metallocene compound is different in nature from the original conventional Ziegler-Natta catalyst so that also the polymers obtained show the typical features associated with the use of metallocene catalysts such as a very narrow Molecular Weight Distribution. As a consequence, the polymerization results showed in the above-cited patent application do not provide any useful teaching about the possible activity of the original catalyst system contained in the pre-polymer.
The European patent application EP-A-604401 proposes the solution of pre-polymerizing a catalyst component, comprising a titanium compound and an electron donor compound supported on a magnesium dihalide, first with a linear olefin and then with a non linear olefin in order to produce a linear olefin/non linear olefin copolymer as a pre-polymer. The so obtained pre-polymer/catalyst system is further contacted with a Ti compound, in particular TiCl4, and optionally also with an electron donor compound in order to obtain a final catalyst component. The pre-polymer/catalyst system obtained however, does not solve the problem because the decrease of the activity observed in the polymerization examples if the activity is calculated as Kg of polymer produced per g of pre-polymer/catalyst fed, is always proportional to the dilution of the catalyst component in the pre-polymer. In other words, when the amount of pre-polymer is about 50% of the total pre-polymer/catalyst system (see Table 2 of EP604401), the activity in the polymerization test is about a half of the activity of the non pre-polymerized catalyst. This means that, according to the disclosure of EP604401, the pre-polymerization step and the further titanation treatment did not improve the activity of the catalyst in itself.
It has now unexpectedly been found a catalyst component having improved activity which is the product obtained by contacting a Ti compound of formula Ti(OR)nxe2x88x92yXy, where R is an alkyl, isoalkyl, cycloalkyl or aryl radical having from 1 to 18 carbon atoms, preferably an alkyl, isoalkyl or cycloalkyl radical having from 1 to 8 carbon atoms. more preferably n-butyl or isopropyl, X is a halogen atom, preferably a chlorine or bromine atom, n is the valence of titanium and y is a number of from 1 to n, with a pre-polymer having a porosity (measured with Hg method) higher than 0.3 cc/g and containing from 0.5 to 100 g of polymer per g of solid catalyst component, said pre-polymer being obtained by (co)polymerizing an olefin or a diolefin which is (co)polymerizable in the presence of a catalyst comprising a solid component comprising a transition metal compound selected from the group consisting of Ti compounds of the above formula Ti(OR)nxe2x88x92yXy, vanadium halides, haloalcoholates and vanadyl halides, Ti, Zr and Hf compounds containing at least a xcfx80-metal bond, said transition metal compound being supported on a Mg dihalide having a mean crystallite size lower than 30 nm.
The porosity of the pre-polymer is preferably higher than 0.4 cc/g and still more preferably higher than 0.5 cc/g. In the present application the term (Hg) porosity referred to the pre-polymer means the porosity measured by the mercury porosimetry method described below and due to pores with radius up to 75,000 xc3x85.
The amount of pre-polymer ranges preferably from 1 to 50 and preferably from 2 to 30 g of polymer per g of solid catalyst component used to prepare it.
The term xe2x80x9cpre-polymerxe2x80x9d used hereabove and hereinafter means a polymer prepared under conditions such as to have a weight ratio polymer/solid catalyst component equal to, or lower than 100; the catalyst used to prepare the pre-polymer being capable to give, under the propylene or ethylene general polymerization conditions given below, a yield higher than 1 Kg/g solid catalyst component.
The magnesium halides, preferably MgCl2, in active form used as a support for Ziegler-Natta catalysts, are well known. The active magnesium halides are those having a mean crystallite size, determined by X-ray diffractometry, lower than 30 nm and particularly preferred are those in which the mean crystallite size is lower than 15 nm. Particularly preferred magnesium chlorides are those characterized by X-ray spectra in which the most intense diffraction line that appears in the spectrum of the non-active chloride is diminished in intensity and is replaced by a halo whose maximum intensity is shifted towards lower angles relative to that of the more intense line.
The preparation of the solid catalyst component used to prepare the pre-polymer can be carried out according to several methods. Preferred methods are those producing catalyst components which, due to their particular physical properties are able to directly produce porous pre-polymers during the pre-polymerization step. In one of the preferred methods the solid catalyst component is prepared by reacting a titanium compound of the general formula Ti(OR)nxe2x88x92yXy as above specified, preferably TiCl4, with an adduct of formula MgCl2.pROH, where p is a number of from 0.1 to 6 and R is a hydrocarbon radical, suitably an alkyl, isoalkyl or cycloalkyl radical, having from 1 to 18, preferably from 1 to 8, more preferably from 1 to 4, carbon atoms. The adduct can be suitably prepared in spherical form by mixing an alcohol of the above formula ROH and magnesium chloride in the presence of an inert hydrocarbon immiscible with the adduct, operating under stirring conditions at the melting temperature of the adduct. Then, the emulsion is quickly quenched, thereby causing the solidification of the adduct in form of spherical particles. Examples of spherical adducts prepared according to this procedure are described in U.S. Pat. Nos. 4,399,054 and 4,469,648. The so obtained adduct can be directly reacted with the Ti compound or it can be previously subjected to thermal controlled dealcoholation (80-130xc2x0 C.) so as to obtain an adduct in which the number of moles of alcohol is generally lower than 3 preferably between 0.1 and 2.5. The reaction with the Ti compound can be carried out for example by suspending the adduct (dealcoholated or as such) in cold TiCl4 (generally 0xc2x0 C.); the mixture is heated up to 80-130xc2x0 C. and kept at this temperature for 0.5-2 hours. The treatment with TiCl4 can be carried out one or more times. When a stereospecific catalyst is to be prepared, an internal electron donor compound is added during the treatment with TiCl4. The treatment with the electron donor compound can be repeated one or more times.
The preparation of catalyst components in spherical form according to the above general procedure is described for example in U.S. Pat. No. 4,399,054, EP-A-395083, EP-A-553805, WO98/44001.
According to another embodiment, the MgCl2.pROH adduct is first thermally dealcoholated according the procedure described above and successively contacted with reactive compounds capable of removing the alcohol. Suitable reactive compounds are, for example, Al-alkyl compounds or SiCl4. The so obtained adduct is then reacted with a titanium compound in order to obtain the final solid catalyst component. The preparation of catalyst components in spherical form according to this procedure is described for example in EP-A-553806, and EP-A-601525.
In general, the solid catalyst components obtained according to the methods described above show a surface area (by B.E.T. method) between 20 and 500 m2/g and preferably between 50 and 400 m2/g, and more preferably between 100 and 400 m2/g; a total porosity (by B.E.T. method) higher than 0.2 cm3/g preferably between 0.2. and 0.6 cm3/g and more preferably from 0.3 to 0.5 cm3/g. The porosity (Hg method) due to pores with radius up to 10,000 xc3x85 generally ranges from 0.3 to 1.5 cm3/g, preferably from 0.45 to 1 cm3/g.
As explained above, when a stereospecific catalyst is desired, an electron donor compound is used in the preparation of the solid catalyst component. The so-called internal electron-donor compound may be selected from esters, ethers, amines and ketones. It is preferably selected from alkyl, cycloalkyl or aryl esters of monocarboxylic acids, for example benzoic acid, or polycarboxylic acids, for example phthalic or malonic acid, the said alkyl, cycloalkyl or aryl groups having from 1 to 18 carbon atoms. Examples of preferred electron-donor compounds are methyl benzoate, ethyl benzoate, diisobutyl phthalate, di-n-hexyl phthalate, di-octyl phthalate, di-neopentyl phthalate. Furthermore, the electron donor compound can be suitably selected from 1,3-diethers of formula (I)
where RI and RII are the same or different and are hydrogen or linear or branched C1-C18 
hydrocarbon groups which can also form one or more cyclic structures; RIII groups, equal or different from each other, are hydrogen or C1-C18 hydrocarbon groups; RIV groups equal or different from each other, have the same meaning of RIIII except that they cannot be hydrogen; each of RI to RIV groups can contain heteroatoms selected from halogens, N, O, S and Si.
Preferably, RIV is a 1-6 carbon atom alkyl radical and more particularly a methyl while the RIII radicals are preferably hydrogen. Moreover, when RI is methyl, ethyl, propyl, or isopropyl, RII can be ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, isopentyl, 2-ethylhexyl, cyclopentyl, cyclohexyl, methylcyclohexyl, phenyl or benzyl; when RI is hydrogen, RII can be ethyl, butyl, sec-butyl, tert-butyl, 2-ethylhexyl, cyclohexylethyl, diphenylmethyl, p-chlorophenyl, 1-naphthyl, 1 -decahydronaphthyl; RI and RII can also be the same and can be ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, neopentyl, phenyl, benzyl, cyclohexyl, cyclopentyl.
Specific examples of ethers that can be advantageously used include: 2-(2-ethylhexyl) 1,3-dimethoxypropane, 2-isopropyl-1,3-dimethoxypropane, 2-butyl- ,3-dimethoxypropane, 2-sec-butyl- 1,3-dimethoxypropane, 2-cyclohexyl- 1,3-dimethoxypropane, 2-phenyl- 1,3-dimethoxypropane, 2-tert-butyl- 1,3-dimethoxypropane, 2-cumyl- 1,3-dimethoxypropane, 2-(2-phenylethyl)-1,3-dimethoxypropane, 2-(2-cyclohexylethyl)-1,3-dimethoxypropane, 2-(p-chlorophenyl)-1,3-dimethoxypropane, 2-(diphenylmethyl)-1,3-dimethoxypropane, 2(1-naphthyl)-1,3-dimethoxypropane, 2(p-fluorophenyl)-1,3-dimethoxypropane, 2(1-decahydronaphthyl)-1,3-dimethoxypropane, 2(p-tert-butylphenyl)-1,3-dimethoxypropane, 2,2-dicyclohexyl-1,3-dimethoxypropane, 2,2-diethyl-1,3-dimethoxypropane, 2,2-dipropyl-1,3-dimethoxypropane, 2,2dibutyl-1,3-dimethoxypropane, 2,2-diethyl-1,3-diethoxypropane, 2,2-dicyclopentyl-1,3-dimethoxypropane, 2,2-dipropyl- 1,3-diethoxypropane, 2,2-dibutyl-1,3-diethoxypropane, 2-methyl-2-ethyl-1,3-dimethoxypropane, 2-methyl-2-propyl-1,3-dimethoxypropane, 2-methyl-2-benzyl-1,3-dimethoxypropane, 2-methyl-2-phenyl- 1,3-dimethoxypropane, 2-methyl-2-cyclohexyl-1,3-dimethoxypropane, 2-methyl-2-methylcyclohexyl-1,3-dimethoxypropane, 2,2-bis(p-chlorophenyl)-1,3-dimethoxypropane, 2,2-bis(2-phenylethyl)-1,3 -dimethoxypropane, 2,2-bis(2-cyclohexylethyl)-1,3-dimethoxypropane, 2-methyl-2-isobutyl-1,3-dimethoxypropane, 2-methyl-2-(2-ethylhexyl)-1,3-dimethoxypropane, 2,2-bis(2-ethylhexyl)-1,3-dimethoxypropane, 2,2-bis(p-methylphenyl)-1,3-dimethoxypropane, 2-methyl-2-isopropyl-1,3-dimethoxypropane, 2,2-diisobutyl-1,3-dimethoxypropane,2,2-diphenyl-1,3-dimethoxypropane, 2,2-dibenzyl-1,3-dimethoxypropane, 2-isopropyl-2-cyclopentyl-1,3-dimethoxypropane, 2,2-bis(cyclohexylmethyl)-1,3-dimethoxypropane, 2,2-diisobutyl-1,3-diethoxypropane, 2,2-diisobutyl-1,3-dibutoxypropane, 2-isobutyl-2-isopropyl- 1,3-dimetoxypropane, 2,2-di-sec-butyl-1,3-dimetoxypropane, 2,2-di-tert-butyl- 1,3-dimethoxypropane, 2,2-dineopentyl-1,3-dimethoxypropane, 2-iso-propyl-2-isopentyl-1,3-dimethoxypropane, 2-phenyl-2-benzyl-1,3-dimetoxypropane, 2-cyclohexyl-2-cyclohexylmethyl-1,3-dimethoxypropane. Particularly preferred are the 1,3-diethers of formula (II) 
where the radicals RIII and RIV have the same meaning explained above and the radicals RV, equal or different to each other, are selected from the group consisting of hydrogen; halogens, preferably Cl and F; C1-C20 alkyl radicals, linear or branched; C3-C20 cycloalkyl, C6-C20 aryl, C7-C20 alkaryl and C7-C20 aralkyl radicals and two or more of the RV radicals can be bonded to each other to form condensed cyclic structures, saturated or unsaturated, optionally substituted with RVI radicals selected from the group consisting of halogens, preferably Cl and F; C1-C20 alkyl radicals, linear or branched; C3-C20 cycloalkyl C6-C20 aryl, C7-C20 alkaryl and C7-C20 aralkyl radicals; said radicals RV and RVI optionally containing one or more heteroatoms as substitutes for carbon or hydrogen atoms, or both. Preferably, in the 1,3-diethers of formulae (I) and (II) all the RIII radicals are hydrogen, and all the RIV radicals are methyl. Moreover, are particularly preferred the 1,3-diethers of formula (II) in which two or more of the RV radicals are bonded to each other to form one or more condensed cyclic structures, preferably benzenic, optionally substituted by RVI radicals. Specially preferred are the compounds of formula (III): 
where the RVI radicals equal or different are hydrogen; halogens, preferably Cl and F; C1-C20 alkyl radicals, linear or branched; C3-C20 cycloalkyl, C6-C20 aryl, C7-C20 alkylaryl and C7-C20 aralkyl radicals, optionally containing one or more heteroatoms selected from the group consisting of N, O, S, P, Si and halogens, in particular Cl and F, as substitutes for carbon or hydrogen atoms, or both; the radicals RIII and RIV are as defined above for formula (II). Specific examples of compounds comprised in formulae (II) and (III) are:
1,1-bis(methoxymethyl)-cyclopentadiene;
1,1-bis(methoxymethyl)-2,3,4,5-tetramethylcyclopentadiene;
1,1-bis(methoxymethyl)-2,3,4,5-tetraphenylcyclopentadiene;
1,1-bis(methoxymethyl)-2,3,4,5-tetrafluorocyclopentadiene;
1,1-bis(methoxymethyl)-3,4-dicyclopentylcyclopentadiene;
1,1-bis(methoxymethyl)indene;
1,1-bis(methoxymethyl)-2,3-dimethylindene;
1,1-bis(methoxymethyl)-4,5,6,7-tetrahydroindene;
1,1-bis(methoxymethyl)-2,3,6,7-tetrafluoroindene;
1,1-bis(methoxymethyl)-4,7-dimethylindene;
1,1-bis(methoxymethyl)-3,6-dimethylindene;
1,1-bis(methoxymethyl)-4-phenylindene;
1,1-bis(methoxymethyl)4-phenyl-2-methylindene;
1,1-bis(methoxymethyl)4-cyclohexylindene;
1,1-bis(methoxymethyl)-7-(3,3,3-trifluoropropyl)indene;
1,1-bis(methoxymethyl)-7-trimethyisilylindene;
1,1-bis(methoxymethyl)-7-trifluoromethylindene;
1,1-bis(methoxymethyl)-4,7-dimethyl-4,5,6,7-tetrahydroindene;
1,1-bis(methoxymethyl)-7- methylindene;
1,1-bis(methoxymethyl)-7-cyclopenthylindene;
1,1-bis(methoxymethyl)-7-isopropylindene;
1,1-bis(methoxymethyl)-7-cyclohexylindene;
1,1-bis(methoxymethyl)-7-tert-butylindene;
1,1-bis(methoxymethyl)-7-tert-butyl-2-methylindene;
1,1-bis(methoxymethyl)-7-phenylindene;
1,1-bis(methoxymethyl)-2-phenylindene;
1,1-bis(methoxymethyl)-1H-benz[e]indene;
1,1-bis(methoxymethyl)-1H-2-methylbenz[e]indene;
9,9-bis(methoxymethyl)fluorene;
9,9-bis(methoxymethyl)-2,3,6,7-tetramethylfluorene;
9,9-bis(methoxymethyl)-2,3,4,5,6,7-hexafluorofluorene;
9,9-bis(methoxymethyl)-2,3-benzofluorene;
9,9-bis(methoxymethyl)-2,3,6,7-dibenzofluorene;
9,9-bis(methoxymethyl)-2,7-diisopropylfluorene;
9,9-bis(methoxymethyl)-1,8-dichlorofluorene;
9,9-bis(methoxymethyl)-2,7-dicyclopentylfluorene;
9,9-bis(methoxymethyl)-1,8-difluorofluorene;
9,9-bis(methoxymethyl)-1,2,3,4-tetrahydrofluorene;
9,9-bis(methoxymethyl)-1,2,3,4,5,6,7,8-octahydrofluorene;
9,9-bis(methoxymethyl)4-tert-butylfluorene.
9,9-bis(methoxymethyl)fluorene being the most preferred.
Most preferred internal electron donors for use in the preparation of the catalyst components of the present invention are the esters of phthalic acid and the above described 1,3 diethers. In the preparation methods described above, the internal electron donor compound can be added as such or, in an alternative way, it can be obtained in situ by using an appropriate precursor capable to be transformed in the desired electron donor compound by means, for example, of known chemical reactions such as esterification or transesterification. Generally, the internal electron donor compound is added in molar ratio with respect to the MgCl2 of from 0.01 to 1 preferably from 0.05 to 0.5.
The solid catalyst components used to prepare the pre-polymer can also be prepared according to the disclosure of WO 95/32995 in which a Ti, Zr or Hf metallocene compound is supported on a MgCl2 having surface area higher than 100 m2/g and porosity (BET) higher than 0.2 cm3/g.
As explained above, the original solid catalyst component is then pre-polymerized with one or more olefins or diolefins to obtain the porous pre-polymer. Generally, the pre-polymer has the same nature as the final polymer to be produced but, if deemed it advisable, the pre-polymer can also have a different nature with respect to the final polymer. This can be the case for example when the pre-polymer has to work as a nucleating agent which is homogeneously dispersed within the final product.
Suitable olefins to be prepolymerized are those of formula CH2xe2x95x90CHR, wherein R is hydrogen or a C1-C12 alkyl group or an aryl radical. Preferably, the olefin is selected from ethylene, propylene, butene-1, hexene-1, and 4-methyl-1-pentene. Ethylene and propylene are especially preferred.
Preferably, the pre-polymer is prepared under conditions such as to obtain a crystalline polymer, and in particular, polymers having a high content of crystallinity. In the case of the pre-polymerization of propylene for example, the preferred polypropylenes are those having a crystallinity such that the fusion enthalpy, measured by DSC method is higher than 70 J/g . The pre-polymerization is generally carried out in the presence of an alkyl-aluminum compound. The alkyl-Al compound (B) is preferably chosen among the trialkyl aluminum compounds such as for example triethylaluminum (TEAL), triisobutylaluminum, tri-n-butylaluminum, tri-n-hexylaluminum, tri-n-octylaluminum. It is also possible to use mixtures of trialkylaluminum""s with alkylaluminum halides alkylaluminum hydrides or alkylaluminum sesquichlorides such as AlEt2Cl and Al2Et3Cl3. It is further possible to use an metallo-alkyl compound different from an alkyl-Al compound, such as zinc di-alkyl compound capable of promoting olefin polymerization when used together with a Ti compound containing Ti-halogen bonds.
When the catalyst components comprise a metallocene compound supported on Mg dihalide, the Al-alkyl is suitably selected from alumoxanes containing the repeating unit xe2x80x94(RI)xe2x80x94Alxe2x80x94Oxe2x80x94 in which RI , equal or different to each other are hydrocarbon groups having from 1 to 20 carbon atoms
The amount of Al-alkyl compound generally used is such as to have an Al/Ti molar ratio of from 1 to 50. In the present invention it has been found particularly advantageous to carry out said pre-polymerization using lower amounts of alkyl-Al compound. In particular, said amount can be as low as to have an Al/Ti molar ratio of from 0.01 to 10 and more preferably of from 0.05 to 5.
During the pre-polymerization step, the presence of an external donor is not strictly necessary. However, it can be used in amounts such as to give Al/donor molar ratios ranging from 0.1 to 300 and preferably from 1 to 50. The external electron donor compound can be the same as, or different from, the internal donor described above. SuiTable external electron donor compounds include silicon compounds, ethers, esters, amines, heterocyclic compounds and particularly 2,2,6,6-tetramethyl piperidine, ketones and the 1,3-diethers of the general formula (I) given above.
A class of preferred external donor compounds, to be used in particular when the internal donor is a phthalate, is that of silicon compounds of formula R5aR6bSi(OR7)c, where a and b are integers of from 0 to 2, c is an integer of from 1 to 3 and the sum (a+b+c) is 4; R5, R6, and R7, are alkyl, cycloalkyl or aryl radicals with 1-18 carbon atoms optionally containing heteroatoms. Particularly preferred are the silicon compounds in which a is 1, b is 1, c is 2, at least one of R5 and R6 is selected from branched alkyl, cycloalkyl or aryl groups with 3-10 carbon atoms optionally containing heteroatoms and R7 is a C1-C10 alkyl group, in particular methyl. Examples of such preferred silicon compounds are methylcyclohexyldimethoxysilane, diphenyldimethoxysilane, methyl-t-butyldimethoxysilane, dicyclopentyldimethoxysilane, 2-ethylpiperidinyl-2-t-butyldimethoxysilane and 1,1,1,trifluoropropyl-2-ethylpiperidinyl-dimethoxysilane. Moreover, are also preferred the silicon compounds in which a is 0, c is 3, R6 is a branched alkyl or cycloalkyl group, optionally containing heteroatoms, and R7 is methyl. Examples of such preferred silicon compounds are cyclohexyltrimethoxysilane, t-butyltrimethoxysilane and thexyltrimethoxysilane.
In particular when esters of monocarboxylic acids, for example benzoates, are used as internal donors also the external donor compound is selected from this class, p-ethoxy-ethyl benzoate being the most preferred. In addition, a mixture of this donor with another one, and in particular one selected from the class of silicon compounds, can be used. In this case ethylcyclohexyldimethoxysilane and dicyclopentyldimethoxysilane are most preferred. The pre-polymerization can be carried out in liquid phase, (slurry or solution) or in gas-phase at temperatures generally lower than 80xc2x0 C., preferably in the range between xe2x88x9220 and 60xc2x0 C. Furthermore, it is preferably carried out in a liquid diluent in particular selected from liquid hydrocarbons. Among them, pentane, hexane and heptane are preferred.
The catalyst component of the present invention is then obtained by contacting the pre-polymer prepared according to the above procedure with the Ti compound as previously defined.
The Ti compound is preferably liquid under normal conditions, i.e. room temperature and atmospheric pressure. When the Ti compound is a solid, it is used in solution in a suitable solvent which is inert towards the pre-polymer and towards the catalyst components contained therein and which can be removed from the Ti compound by heating and/or chemical reaction with compounds such as SiCl4 or Al-alkyl compounds.
Preferably, the Ti compound is selected from the group consisting of halides and, among them, the use of TiCl4 is especially preferred.
The contact of the pre-polymer with the Ti compound is carried out under conditions suitable to fix at least 0.05% of Ti compound, expressed as Ti, on the pre-polymerized catalyst component. A Ti compound is considered fixed on the pre-polymerized catalyst component when it is not extractable to an extent higher than 50% with heptane at 80xc2x0 C. for 2 hours. The amount of Ti compound fixed on the pre-polymerized catalyst component by effect of the contact stage is generally higher than 0.05%, preferably higher than 0.2%, expressed as Ti.
In particular, when a Ti-based catalyst component is used to prepare the pre-polymer, the total amount of Ti compound (expressed as Ti) after the contact stage is from 0.1 to 5% preferably from 0.15 to 3% and more preferably from 0.2 to 2,5%.
In this case, particularly advantageous are the catalyst components containing Mg dichloride in amount of 50 to 50,000 ppm, expressed as Mg, and in which the total amount of Ti compound fixed on the pre-polymerized catalyst component is such as to have a Ti/Mg weight ratio of from 0.01 to 3.and preferably from 0.1 to 2.5.
According to one of the preferred methods the pre-polymer is reacted with an excess of neat TiCl4 at a temperature between 40 and 120xc2x0, preferably from 60 and 90xc2x0 C. for a period of time ranging from 0.2 to 2 h. At the end of the treatment the excess of TiCl4 is removed by siphoning or filtration of the solid component. Preferably, the reaction with TiCl4 is carried out two or more times. Moreover, it is especially preferred carrying out said reaction in the presence of an electron donor compound dissolved in the TiCl4. Preferably, the electron donor compound is selected from the groups disclosed above as suitable internal electron donor compounds.
According to another method the reaction is carried out with TiCl4 diluted in a suitable hydrocarbon compound such as pentane, hexane, heptane, toluene. Also in this case the use of an internal electron donor compound is preferred.
After the contact stage with the Ti compound is completed the pre-polymerized catalyst component is suitably washed with solvents, in order to remove compounds not fixed on it. The washings are generally carried out at temperatures comprised between the room temperature and the boiling point of the solvent used. Suitable solvents to be used include liquid hydrocarbons such as hexane, heptane, toluene and halogenated hydrocarbons such as CH2Cl2.
The thus obtained pre-polymerized catalyst components allow to obtain highly active catalysts. In particular, when used in the polymerization of propylene, allow to obtain polymers with high stereoregularity, high bulk density and very good morphology thus showing their particular suitability for the liquid (bulk or slurry) and gas-phase processes. In particular, the pre-polymerized catalyst components of the invention show activities referred to the Mg that are remarkably improved with respect to those of the original solid component used to prepare the pre-polymer. Also, the yields referred to the pre-polymer/catalyst system are higher than the yields of the pre-polymer catalyst/system not treated with the Ti compound.
In view of these peculiarities, the catalyst components of the invention are particularly suitable for the use in liquid or gas-phase olefin polymerization plants operating without a pre-polymerization line.
In particular, said olefin polymerization processes are be carried out in the presence of a catalyst comprising (A) the pre-polymerized catalyst component described above; (B) a suitable cocatalyst, particularly an Al-alkyl compound, and optionally (C) one or more electron donor (external) compounds.
These latter can be selected from the groups of compounds that have been disclosed above as suitable external electron compounds and according to the guidance already described. In the main polymerization step the electron donor compound (C) is used in such an amount to give a molar ratio between the organoaluminum compound and said electron donor compound of from 0.1 to 500, preferably from 1 to 300 and more preferably from 2 to 100. The Al/Ti ratio is preferably higher than 10.
The Al-alkyl compounds are preferably selected from those of formula RzAlX3-z, in which R is a C1-C20 hydrocarbon group, particularly an alkyl, isoalkyl, cycloalkyl or aryl radical, z is 2 or 3 and X is an halogen atom, preferably chlorine. Particularly preferred is the use of the trialkyl aluminum compounds such as for example triethylaluminum (TEAL), triisobutylaluminum, tri-n-butylaluminum, tri-n-hexylaluminum, tri-n-octylaluminum and tris(2,4,4-trimethyl-pentyl)aluminum. It is also possible to use mixtures of trialkylaluminum compounds with alkylaluminum halides, alkylaluminum hydrides or alkylaluminum sesquichlorides, such as AlEt2Cl and Al2Et3Cl3.
Another class of compounds suitable as catalyst components to prepare the pre-polymer is that of the metallocene compounds having at least one Mxe2x80x94R link in which M is Ti, Zr, or Hf and R is an alkyl radical. Said metallocene compounds are used in amounts such as to be in an equimolar ratio or in excess with respect to the metal compound present in the catalyst component. Preferably, said ratio ranges from 2:1 to 30:1. In case an equimolar amount of cocatalyst is used it is preferred adding a scavenger compound to the system selected from Al, Mg or Zn alkyl compounds that are not able to promote olefin polymerization when employed together with compounds containing Ti-halogen bonds. Examples of these compounds are Zn diethyl, Mg diethyl and AlEt3 complexed with ethers or electron donor compounds not containing active hydrogen atoms.
Suitable metallocene compounds having at least one Mxe2x80x94R link are generally those comprising two cyclopentadienyl rings, coordinated with the metal, which can be substituted and/or bridged and possibly condensed with other rings. Representative compounds are specifically mentioned and described in WO95/26369 the relevant part of which is herein included by reference.
In case the catalyst components comprise a metallocene compound, it is advisable to use, alone or in combination with another Al-alkyl compound, an alumoxane selected from those containing the repeating unit xe2x80x94(R1)xe2x80x94Alxe2x80x94Oxe2x80x94 in which R1, equal or different to each other are hydrocarbon groups having from 1 to 20 carbon atoms. The use of methylalumoxane is preferred. In addition, it is also possible to use compounds of the formula Y+Zxe2x88x92, where Y+ is a Brxc3x6nsted acid capable of donating a proton and irreversibly reacting with a substituent of the metallocene compound, and Zxe2x88x92 is a compatible not coordinating anion which is capable of stabilizing the active catalytic species resulting from the reaction of the two compounds and which is sufficiently labile to be displaced by an olefinic substrate. Preferably, the anion Zxe2x88x92 consists of one or more boron atoms. More preferably, the anion Zxe2x88x92 is an anion of the formula BAr4xe2x88x92, where the substituents Ar which can be identical or different are aryl radicals such as phenyl, pentafluorophenyl or bis(trifluoro-methyl)phenyl. Tetrakis-pentafluorophenyl borate is particularly preferred. Moreover, compounds of the formula BAr3 can conveniently be used. Compounds of this type are described for example, in the International patent application WO92/00333.
The above described polymerization process can be carried out under the polymerization conditions generally known in the art. Accordingly, the polymerization is generally carried out at a temperature of from 20 to 120xc2x0 C., preferably of from 40 to 80xc2x0 C. When the polymerization is carried out in gas-phase the operating pressure is generally between 0.5 and 10 MPa, preferably between 1 and 5 MPa. In the bulk polymerization the operating pressure is generally between 1 and 6 MPa preferably between 1.5 and 4 MPa.
In any of the polymerization processes used (liquid or gas-phase polymerization) the catalyst forming components (A), (B) and optionally (C), can be pre-contacted before adding them to the polymerization reactor. Said pre-contacting step can be carried out in the absence of polymerizable olefin or optionally in the presence of said olefin in an amount up to 3 g per g of solid catalyst component. The catalyst forming components can be contacted with a liquid inert hydrocarbon solvent such as propane, n-hexane, or n-heptane at a temperature below about 60xc2x0 C. and preferably from about 0xc2x0 C. to 30xc2x0 C. for a time period of from 10 seconds to 60 minutes.
When a gas-phase polymerization process is used, it can be carried out according to known techniques operating in ore or more reactors having a fluidized or mechanically agitated bed. Inert fluids such as nitrogen, or low hydrocarbons like propane, can be used both as a fluidization aid and in order to improve the thermal exchange within the reactors. In addition, also techniques increasing the removal of the reaction heat comprising the introduction of liquids, optionally in mixture with gas, into the reactors, can be used. Preferably the liquids are fresh or make-up monomers. Such techniques are disclosed for example in EP-A-89691, EP-A-241947, U.S. Pat. No. 5,352,749, WO94/28032 and EPA-695313.
Among the olefin polymers obtainable by the process of the invention, particularly interesting are the propylene (co)polymers having a heat of fusion (xcex94Hf) higher than 70 J/g measured by D.S.C. method.